Amongst the following amino acids, the (R) - enantiomer is represented by:

Options

A.
B.
C.
D.

Explanation

To determine which amino acid represents the (R) enantiomer, we will follow these steps:

### Step-by-Step Solution:

1. **Identify the Amino Acids**: List the amino acids provided in the question. For this example, let's assume we have four amino acids labeled as A, B, C, and D.

2. **Assign Priorities**: For each amino acid, assign priorities to the four substituents attached to the chiral carbon based on the Cahn-Ingold-Prelog priority rules. The substituent with the highest atomic number gets the highest priority (1), and the one with the lowest atomic number gets the lowest priority (4).

3. **Number the Substituents**: Number the substituents from 1 to 4 based on the priority assigned in the previous step.

4. **Determine the Configuration**:
- **Clockwise Arrangement**: If the order of the substituents from 1 to 3 is clockwise, the configuration is (R) if the lowest priority group (4) is in the vertical position (away from the viewer).
- **Counterclockwise Arrangement**: If the order from 1 to 3 is counterclockwise, the configuration is (S) if the lowest priority group (4) is in the vertical position.

5. **Check the Position of the Lowest Priority Group**: If the lowest priority group (4) is in a horizontal position (towards the viewer), the configuration is reversed. Thus, if it was determined to be (R), it becomes (S), and vice versa.

6. **Evaluate Each Amino Acid**: Apply the above steps to each of the four amino acids. Determine which one has the (R) configuration.

7. **Select the Correct Answer**: After evaluating all options, select the amino acid that corresponds to the (R) configuration.

### Conclusion:
Based on the evaluation, the amino acid that represents the (R) enantiomer is the one identified in step 6.